This invention relates to a new class of nickel and palladium complexes useful in the (co)polymerization of olefins.
It has been recently discovered that complexes of nickel or palladium with alpha-diimine ligand can be used as catalysts for polymerizing olefins; for instance WO 96/23010 discloses with several examples various types of these complexes, showing that they can be used for polymerizing a large number of olefins.
Immobilizing these complexes on solid supports to enable heterogeneous polymerization processes, such as those based on gas-phase, bulk or slurry processes, is important for their efficient industrial utilization. In particular, some non supported nickel catalysts give rise to polymers characterized by a high level of branching. The melting points of these polymers are anticipated to be as low as to present problems with reactor operation at typical industrial operating temperatures, especially when heat dissipation by solvents is unavailable, as in continuous gas phase polymerization.
WO 96/23010 discloses supported diimine palladium or nickel catalysts. It exemplifies a process wherein a complex activated with a cocatalyst is adsorbed on silica.
WO 97/48736 relates to immobilized catalysts; they are substantially obtained by preparing a precursor solution mixing together the complex with an aluminoxane and adding this precursor solution to a porous support.
In some examples of WO 98/56832 the cocatalyst was supported on an inorganic support and then a diimino-complex was added, then the obtained catalyst was prepolymerized.
For avoiding the drawback of the migration of the active species into the homogeneous phase during the polymerization reaction, a chemical bond between the carrier and the diimino-complex could be desirable.
An object of the present invention is a bidentate diimino-complex of nickel or palladium containing a siloxy group, that can be easily supported on a carrier through a chemical bond between the carrier and the complex itself.
Another object of the present invention is an olefin polymerization catalyst comprising as catalyst component a diimino-complex of nickel or palladium containing a siloxy group.
A further object of the present invention is a solid polymerization catalyst comprising the diimino-complex of nickel or palladium object of the present invention, a carrier and a cocatalyst.
In this solid catalyst, the catalytic centres are attached to the support by means of the alkoxysilane functionality, thus providing a true heterogeneous catalyst. The preparation of said catalyst precursor results in little or no contaminating secondary reaction products, hence the catalyst is substantially or completely free from undesirable impurities. The catalysts can be used in solution, high pressure, slurry or gas-phase processes. The catalysts are especially useful for the production of branched polyethylene without requiring co-monomer.
The present invention relates to a bidentate diimino-complex of nickel or palladium containing at least one group OSi(R)3 wherein each R, equal to or different from each other, is selected from the group consisting of: C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C2-C20 alkenyl, C7-C20 arylalkyl, C7-C20 alkylaryl, C8-C20 arylalkenyl, and C8-C20 alkenylaryl, linear or branched, preferably each R is independently methyl, ethyl or propyl.
The present invention also relates to the process for the preparation of bidentate diimino complexes of nickel and palladium as well as the process for their use in olefin polymerization.
The present invention relates to a bidentate diimino-complex of nickel or palladium containing at least one group OSi(R)3 wherein each R, equal to or different from each other, is selected from the group consisting of: C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C2-C20 alkenyl, C7-C20 arylalkyl, C7-C20, alkylaryl, C8-C20 arylalkenyl, and C8-C20 alkenylaryl, linear or branched, preferably R is methyl, ethyl or propyl. Preferably the bidenitate diimino-complex of nickel and palladium is defined by the following general formulas: 
wherein
M is nickel or palladium, n is 0, 1, 2 or 3; m is 1, 2 or 3,
each X, equal to or different from each other, is independently selected from the group consisting of: halogen, hydrogen, OR, N(R)2, R, wherein each R is independently selected from the group consisting of: C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C2-C20 alkenyl, C7-C20 arylalkyl, C7-C20 alkylaryl, C8-C20 arylalkenyl, and C8-C20 alkenylaryl; linear or branched, preferably each R is independently methyl, ethyl or propyl; two X taken together can also form an aromatic or aliphatic divalent ligand, containing two equal or different donor atoms belonging to the group 14-16 of the periodic table of the elements, such as catecholate, 1,2-ethanediolate or 1,2-phenylenediamide, xcex1-deprotonated-xcex2-diketone, xcex1-deprotonated-xcex2-ketoester such as acetylacetonate or hexafluoracetylacetonate;
each R1, equal to or different from each other, is selected from the group consisting of: hydrogen, a monovalent aliphatic or aromatic hydrocarbon group, optionally containing heteroatoms of group 14 to 16 of the periodic table of the elements or boron; with the proviso that at least one R1 group is represented by the formula: R4OSi(R)3;
wherein
each R4, equal to or different from each other, is a divalent aliphatic or aromatic hydrocarbon group containing from 1 to 20 carbon atoms, optionally containing from 1 to 5 heteroatoms of groups 14 to 16 of the periodic table of the elements and/or boron;
preferably it is CR52(R6)aCR52,
wherein
each R5, equal to or different from each other, is selected from the group consisting of: hydrogen and R; two R5 can also unite to form a ring;
R6 is a divalent radical selected from the group comprising: O, NR, S, SiR52, C1-C20 alkylidene, C3-C20 cycloalkylidene, C2-C20 alkenylidene, C6-C20 arylidene, C7-C20 alkylarylidene, C7-C20 arylalkylidene, C8-C20 arylalkylidene, or C8-C20 alkenylarylidene, linear or branched, optionally containing heteroatoms of group 14 to 16 of the periodic table of the elements, and/or boron;
a is 0 or 1;
each R2, equal to or different from each other, is a radical which contains from 1 to 20 carbon atoms; this group optionally contains heteroatoms of group 14 to 16 of the periodic table of the elements and boron;
preferably each R2 is independently selected from the group consisting of: C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C2-C20 alkenyl, C7-C20 arylalkyl, C7-C20 alkylaryl, C8-C20 arylalkenyl, C8-C20 alkenylaryl, linear or branched, optionally substituted by BR52, OR5, SiR53, or NR52, most preferably R2 is a alkylsubstituted phenyl, naphthyl or anthracyl, most preferably R2 is a 2,6 dialkylphenyl group, optionally substituted in position 4 by a group R as defined above.
each R3, equal to or different from each other, is hydrogen or a radical which contains from 1 to 20 carbon atoms; this group optionally contains heteroatoms of group 14 to 16 of the periodic table of the elements and/or boron;
preferably R3 is independently selected from the group consisting of: hydrogen, C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C2-C20 alkenyl, C7-C20 arylalkyl, C7-C20 alkylaryl, C8-C20 arylalkenyl, and C8-C20 alkenylaryl, linear or branched, optionally substituted by BR52, OR5, SiR53, or NR52 where R5 is defined above;
two or more R1, R2, R3 and R4 can also unite to form a from 4 to 15 membered aliphatic or aromatic ring; the ring optionally contains heteroatoms of group 14 to 16 of the periodic table of the elements and boron.
Preferably R1 is selected from the group consisting of: hydrogen; C1-C20 alkyl; C3-C20 cycloalkyl; C6-C20 aryl; C2-C20 alkenyl; C7-C20 arylalkyl; C7-C20 alkylaryl; C8-C20 arylalkenyl; and C8-C20 alkenylaryl; linear or branched, optionally substituted by BR52, OR5, SiR53, NR52; or R4OSi(R)3 where R4 and R5 are defined above;
examples of group CR52(R6)aCR52 OSi(R)3 are:
xe2x80x94CH2xe2x80x94CH2xe2x80x94OSiMe3; xe2x80x94CH2xe2x80x94(CH2)pxe2x80x94CH2xe2x80x94OSiMe3 wherein p ranges from 1 to 10;
xe2x80x94CH2xe2x80x94Oxe2x80x94CH2xe2x80x94OSiMe3; xe2x80x94CH2xe2x80x94C6H4xe2x80x94CH2xe2x80x94OSiMe3; xe2x80x94CH(Et)xe2x80x94CH2xe2x80x94OSi(Et)2Me;
xe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94CH2OSi(iPr)3; xe2x80x94CH2xe2x80x94Si(CH3)2xe2x80x94CH2OSi(iPr)3;
xe2x80x94CH2xe2x80x94CH2xe2x80x94Si(CH3)2xe2x80x94CH2OSi(iPr)3; xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94N(CH3)xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2OSi(iPr)3;
xe2x80x94C(Me)2xe2x80x94CH2xe2x80x94C6H4xe2x80x94CH2xe2x80x94CH2xe2x80x94OSi(C5H11)3; xe2x80x94CH2xe2x80x94CH2xe2x80x94C6H4xe2x80x94C6H4Oxe2x80x94CH2xe2x80x94CH2xe2x80x94OSi(CH2Ph)3;
xe2x80x94C(CH3)2xe2x80x94C(CH3)2xe2x80x94OSi(C6H4Me)3; xe2x80x94CH(Me)xe2x80x94CH(Me)xe2x80x94OSi(Et)(Me)2.
Compounds of general formula I and II, wherein the group R4OSi(R)3 is CR52(R6)aCR52OSi(R)3, can be prepared by a process comprising the following steps:
1) reacting a compound represented by formula III or IV 
wherein each Z is independently selected from the group consisting of R1 and CR52H provided that at least one Z is CR52H; with a Bronsted base preferably selected from the group consisting of: organolithium compound, organosodium compounds, organopotassium compounds, oranomagnesium compounds, sodium hydride, potassium hydride, lithium, sodium, or potassium; preferably lithium alkyl, sodium alkyl, potassium alkyl; more preferably butyllithium;
2) contacting the obtained metallated compound with one equivalent of a compound of general formula Y(R6)nCR52OSi(R)3 (as defined above) and wherein Y is a leaving group, preferably halogen, sulfonate groups, more preferably iodine or bromine, and
3) reacting the obtained product with a compound of general formula LqMX2, wherein M and X have already been defined; L is a labile ligand, i.e. is a weakly coordination group that is removed during the reaction, for example L is a neutral Lewis base such as diethylether, tetrahydrofurane, dimethylaniline, aniline, triphenilphosphine, n-butylamine; 1,2 dimethoxyethane (DME) cyclooctadiene, pyridine, 1,1,2,2-tetramethylendiamine, aromatic or aliphatic nitriles, sulphides, sulphoxides or tioles, triaryl phosphines, arsines or stibines; and q is 1 or 2.
While not wishing to be bound by theory, it is believed that in the above procedure, advantage has been taken of acidity of hydrogen atoms bonded at a carbon in the alpha position to the imino group. Thus, it is believed that following a selection of the base to be used, one acidic proton at the carbon atom at the alpha position of the imino group is removed, resulting in an anionic specie which is believed to be prone to act as a nucleophile in the presence of an electrophile. Thus a new bond can be formed when these two species interact. It is commonly known that such a new bond can be formed through two general pathways: by substitution or by addition. In the first case a leaving group is detached from the electrophilic centre. In the second case, a bond is broken (for instance a double bond becomes a single bond).
In order to have the desired alkoxysilane functional group in the final ligand thus formed, the functional group, or a suitable precursor of it, is preferably already present in the electrophile.
According to this synthetic procedure, choosing an appropriate base is desirable in order to selectively remove a hydrogen atom from the carbon atom in alpha to the imino group and, at the same time, not promoting undesired secondary reactions (for instance addition to the imine double bond). Also a suitable leaving group Y is preferably introduced in the electrophile in order to facilitate the formation of the new bond.
The synthetic method of the present invention has also the advantage of providing the possibility of linking more than just one functional group as long as there are more hydrogen atoms at the carbon atom in an alpha position to any of the two imine groups in the diimine precursor. It is sufficient to adjust the amount of base to be added to the original diimine in order to remove the desired number of hydrogen atoms.
Non limiting examples of compounds represented by formula YR5(CR67)nOSi(R)3 are:
Clxe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94CH2xe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94(CH2)2xe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94(CH2)3xe2x80x94CH2xe2x80x94OSiMe3,
Clxe2x80x94(CH2)4xe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94(CH2)5xe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94CH3xe2x80x94(CH2)6xe2x80x94CH2xe2x80x94OSiMe3,
Clxe2x80x94(CH2)7xe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94C6H4xe2x80x94CH3xe2x80x94OSiMe3, Clxe2x80x94(CH2)8xe2x80x94CH2xe2x80x94OSiMe3,
Clxe2x80x94(CH2)9xe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94(CH2)10xe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94CH2xe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiMe3,
Clxe2x80x94CH2xe2x80x94CMe2xe2x80x94CH2xe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94CH2xe2x80x94CMe2xe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiMe3,
Clxe2x80x94CH2xe2x80x94C6H4xe2x80x94Oxe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94CH2xe2x80x94CEtMexe2x80x94CH2xe2x80x94OSiMe3,
Clxe2x80x94CH2xe2x80x94CEt2xe2x80x94CH2xe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94CH2xe2x80x94CMe2xe2x80x94CEt2xe2x80x94CH2xe2x80x94OSiMe3,
Clxe2x80x94CH2xe2x80x94C6H4xe2x80x94Oxe2x80x94CH2xe2x80x94OSiMe3, Clxe2x80x94CEt2xe2x80x94CH2xe2x80x94OSiMe3,
Brxe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94CH2xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94(CH2)2xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94(CH2)3xe2x80x94CH2xe2x80x94OSiMe3,
Brxe2x80x94(CH2)4xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94(CH2)5xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94(CH2)6xe2x80x94CH2xe2x80x94OSiMe3,
Brxe2x80x94(CH2)7xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94CH2xe2x80x94C6H4xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94(CH2)8xe2x80x94CH2xe2x80x94OSiMe3,
Brxe2x80x94(CH2)9xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94(CH2)10xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94CH2xe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiMe3,
Brxe2x80x94(CH2xe2x80x94CMe2xe2x80x94CH2xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94CH2xe2x80x94CMe2xe2x80x94CM2xe2x80x94CH2xe2x80x94OSiMe3,
Brxe2x80x94CH2xe2x80x94C6H4xe2x80x94Oxe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94CH2xe2x80x94CEtMexe2x80x94CH2xe2x80x94OSiMe3,
Brxe2x80x94CH2xe2x80x94CEt2xe2x80x94CH2xe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94CH2xe2x80x94CMe2xe2x80x94CEt2xe2x80x94CH2xe2x80x94OSiMe3,
Brxe2x80x94CH2xe2x80x94C6H4xe2x80x94Oxe2x80x94CH2xe2x80x94OSiMe3, Brxe2x80x94CEt2xe2x80x94CH2xe2x80x94OSiMe3,
Ixe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94CH2xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94(CH2)2xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94(CH2)3xe2x80x94CH2xe2x80x94OSiMe3,
Ixe2x80x94(CH2)4xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94(CH2)5xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94(CH2)6xe2x80x94CH2xe2x80x94OSiMe3,
Ixe2x80x94(CH2)7xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94CH2xe2x80x94C6H4xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94(CH2)8xe2x80x94CH2xe2x80x94OSiMe3,
Ixe2x80x94(CH2)9xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94(CH2)10xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94CH2xe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiMe3,
Ixe2x80x94CH2xe2x80x94CMe2xe2x80x94CH2xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94CH2xe2x80x94CMe2xe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiMe2, Ixe2x80x94CH2xe2x80x94C6H4xe2x80x94Oxe2x80x94CH2xe2x80x94OSiMe3,
Ixe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94CH2xe2x80x94CEtMexe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94CH2xe2x80x94CEt2xe2x80x94CH2xe2x80x94CH2xe2x80x94OSiMe3,
Ixe2x80x94CH2xe2x80x94CMe2xe2x80x94CEt2xe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94CH2xe2x80x94C6H4xe2x80x94Oxe2x80x94CH2xe2x80x94OSiMe3, Ixe2x80x94CEt2xe2x80x94CH2xe2x80x94OSiMe3,
Ixe2x80x94CH2xe2x80x94OSiEt3, Ixe2x80x94CH2xe2x80x94CH2xe2x80x94OSiEt3, Ixe2x80x94(CH2)2xe2x80x94CH2xe2x80x94OSiEt3, Ixe2x80x94(CH2)3xe2x80x94CH2xe2x80x94OSiEt3,
Ixe2x80x94(CH2)4xe2x80x94CH2xe2x80x94OSiEt3, Ixe2x80x94(CH2)5xe2x80x94CH2xe2x80x94OSiEt3, Ixe2x80x94(CH2)6xe2x80x94CH2xe2x80x94OSiEt3,
Brxe2x80x94(CH2)7xe2x80x94CH2xe2x80x94OSiPr3, Brxe2x80x94CH2xe2x80x94C6H4xe2x80x94CH2xe2x80x94OSiPr3, Brxe2x80x94(CH2)8xe2x80x94CH2xe2x80x94OSiPr3,
Brxe2x80x94(CH2)9xe2x80x94CH2xe2x80x94OSiPr3, Brxe2x80x94(CH2)10xe2x80x94CH2xe2x80x94OSiPr3, Brxe2x80x94CH2xe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiPr3,
Clxe2x80x94CH2xe2x80x94CMe2xe2x80x94CH2xe2x80x94CH2xe2x80x94OSiPh3, Clxe2x80x94CH2xe2x80x94CMe2xe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiPh3,
Clxe2x80x94CH2xe2x80x94C6H4xe2x80x94Oxe2x80x94CH2xe2x80x94OSiPh3, Clxe2x80x94CMe2xe2x80x94CH2xe2x80x94OSiPh3, Clxe2x80x94CH2xe2x80x94CEtMexe2x80x94CH2xe2x80x94OStPh3,
Clxe2x80x94CH2xe2x80x94CEt2xe2x80x94CH2xe2x80x94CH2xe2x80x94OSiPh3, Brxe2x80x94CH2xe2x80x94CMe2xe2x80x94CEt2xe2x80x94CH2xe2x80x94OSiMeEt2,
Brxe2x80x94CH2xe2x80x94C6H4xe2x80x94Oxe2x80x94CH2xe2x80x94OSiPhMe2, Brxe2x80x94CEt2xe2x80x94CH2xe2x80x94OSiEtPr2.
More preferred diimino compounds of formula I are: 
Non limitative examples of compounds according to formula 1 are: 
The compounds of the present invention can be used as catalyst components for polymerizing olefins, preferably alpha-olefins. This catalyst component is especially useful for the production of branched polyethylene without requiring co-monomer. The catalyst component of the present invention is preferably used in combination with a cocatalyst. Illustrative but non-limiting examples of co-catalysts are: aluminoxanes (methylaluminoxane (MAO), modified methylaluminoxane (MMAO), isobutylaluminoxane (IBAO), etc.), combinations of alkylaluminiums (such as trimethylaluminium, trimethylaluminium, tributylaluminium, etc.) and boron containing Lewis acids (such as trifluoroborate, trispentafluorophenylborane, tris[3,5-bis(trifluoromethyl)phenyl]borane, etc.), hydrogen Lewis acids (dimethylanilinium tetrakis(pentafluorophenyl)boron, HBF4, etc.), silver Lewis acids (such as AgBF4, AgPF6, AgSbF6, silver tetrakis[3,5-bis(trifluoromethyl)phenyl]borate etc.) or others (such as sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, etc.).
The catalyst component of the present invention is especially useful for being supported on a porous inorganic solid. As supporting material, any type of inorganic oxides can be used, such as: silica, alumina, silica-alumina, aluminum phosphates and mixtures thereof, obtaining supported catalysts with contents in transition metals between 0.01 and 10% by weight, preferably between 0.1 and 4%. Particularly preferred supports are silica calcined at a temperature between 600xc2x0 C. and 800xc2x0 C., and silica previously treated with alumoxane.
A process for preparing supported catalysts according to this invention comprises the following steps:
a) contacting, preferably under anhydrous conditions and inert atmosphere, a solution of at least one diimino-complex of the present invention, with the support material at a temperature between xe2x88x9220xc2x0 C. and 90xc2x0 C.; and
b) filtering and washing with a solvent, selected from aliphatic or aromatic hydrocarbon, or a mixture thereof.
Another process that can be used comprises the following steps:
a) contacting, preferably under anhydrous conditions and inert atmosphere, a solution of at least one diimino-complex of the present invention, with the support material at a temperature between xe2x88x9220xc2x0 C. and 90xc2x0 C.;
b) eliminating the solvent preferably through evaporation;
c) warming the solid residue up to temperature between 25 and 150xc2x0 C.
The solid catalyst obtained by this process can be further subjected to washing and subsequent filtration.
The amount of the diimino-complex which can be anchored onto the support with the above methods directly relates to the concentration of the reactive groups present in the support. For this reason silica, for example, should preferably have been calcinated at a temperature between 600xc2x0 C. and 800xc2x0 C., preferably in a dry atmosphere.
An advantageous aspect of this invention is that the support method, presumably as a consequence of the reaction of group xe2x80x94OSi(R)3 with reactive groups of the support surface, appears to prevent the desorption of the supported diimino-complexes. This type of interaction represents a significant difference between the organo-complexes heterogenization mechanism and other conventional methods, where the diimino-complex generally remains physisorbed on the support surface.
The procedure employed for the formation of the catalyst results in little or no by-products that could hamper the polymerisation process. Thus, no extra reactants other than the functionalized complex and the silica are needed. Thus, in a preferred embodiment, scavengers and other agents to neutralize the by-products are not used.
The choice of diimino ligand and metal can result in a highly active catalyst for the polymerisation of olefins. The properties of the polyolefins so obtained can be finely tuned by a selection of the structural properties of the diimine ligand attached to the silica, the nature of the metal centre employed and the polymerisation conditions used (e.g. temperature, pressure, concentration of reactants, etc.).
A solid catalyst system can be obtained by adding to the solid catalyst component a cocatalyst, for example alumoxane, boron compounds or mixtures thereof, at any step of the processes described above. For example, catalyst systems can be obtained by reacting silica with the bidentate diimino-complex and then adding alumoxane or treating silica with alumoxane and then reacting the obtained carrier with the bidentate diimino-complex.
For the polymerization in solution, the cocatalyst can be mixed with a solution of a diimino-complex of formula I or II and a supplementary quantity of cocatalyst can be added to the solution; or the catalyst can directly be added to the polymerization medium, which contains the cocatalyst.
For the polymerization in suspension, the cocatalyst can previously be mixed with the supported solid catalyst or it can be added to the polymerization medium before the supported catalyst, or both operations can be sequentially realized.
The most useful polymerization procedure can change according to the chosen type of polymerization process (solution, suspension, slurry or gas phase).
In general, the process comprises contacting the monomer, or, in certain cases, the monomer and the comonomer, with a catalytic composition according to the present invention, that includes at least one diimino-complex of formula I or II.
The alpha-olefins that can be used as comonomers to obtain ethylene copolymers can be one or more C3-C12 linear or branched alpha olefin, such as propylene, butene, hexene, octene and 4-methyl-1-pentene and can be used in proportions from 0.1 to 70% by weight of the total of the monomers. In the case of polymerization of ethylene the density of polymers can be as low as 0.86 g/cm3.
In the particular case of gas-phase suspension process or controlled particle morphology process, the used temperature will be preferably between 30xc2x0 and 100xc2x0 C., while for the solution process the usual temperature will be between 120xc2x0 and 250xc2x0 C.
The pressure will change according to the polymerization technique and may range from atmospheric pressure to 350 MPa.